Mark Clattenburg has spoken of his relief at being cleared of directing a racist comment towards the Chelsea midfielder Mikel John Obi, describing the allegations as the most frightening experience of his life.

As Chelsea prepared to unveil Rafael Benítez as their new interim manager, the club was informed by the Football Association that Clattenburg did not have a case to answer.

Prospect, the referee's union, has demanded a full apology, compensation and a donation to an anti-racism charity from Chelsea. Others have raised the possibility of Clattenburg taking legal action against the club.

Mikel has been charged by the FA with using threatening or abusive words and/or behaviour following Chelsea's dramatic home defeat to Manchester United, during which Fernando Torres and Branislav Ivanovic were sent off.

The club said that while Mikel, who could face a three-match ban, did not deny the charge against him he would request a personal hearing.

Clattenburg paid tribute to the support of his colleagues and said he "couldn't wait" to get back to refereeing. "The messages of encouragement from those inside and outside of the game have helped me through the most stressful time of my professional life. To know you were innocent of something but that there was the opportunity for it to wreck your career was truly frightening," said the official, who has been absent from the referee's list for the past four weekends.

"Racism has no place in football and this experience should not discourage those to speak out if they genuinely believe they are a victim of abuse. However, there are processes that should be adhered in order that any investigation can be carried out in a manner that is fair for all parties involved."

Ramires claimed that he had heard Clattenburg call Mikel a "monkey", but neither Clattenburg nor the three other match officials, who could hear everything being said in their earpieces, heard the comment. The FA said that neither Mikel, who was much closer to the referee than Ramires, heard what it is suggested was said to him. Nor was there anything in the video evidence to support the allegation and nor did two other players, whose first language is English, hear anything untoward.

"Having considered all of the available evidence it was the opinion of David Waters QC, independent counsel, that the evidence of Ramires was not supported by any other evidence. Moreover it was contradicted by other witnesses and does not cross the evidential threshold required to bring a charge against Mark Clattenburg," the FA said. "Having considered counsel's opinion, and in view of all the circumstances of the case, the FA does not believe that there is a case for Mr Clattenburg to answer."

The Professional Game Match Officials Limited general manager, Mike Riley, said that in light of the incident, all communications between referees would now be recorded.

"It is PGMOL's considered view that Mark is completely exonerated of the allegation and he will return to active duty shortly without any stain on his character or reputation," Riley said. "The verbal and visual facts do not support any of the allegations made against him. They make it clear that Mark did not use any inappropriate language towards any Chelsea player."

It is understood that neither Clattenburg nor his colleagues recall him using any language that could have been misheard by Ramires as "monkey". However, the FA underlined that it believed the Brazilian had acted in good faith.

Chelsea, under intense pressure following criticism of their handling of the fallout from John Terry's four-match ban for racially abusing QPR's Anton Ferdinand, said they accepted the FA's verdict but defended their decision to pursue the complaint.

"Chelsea FC has a duty of care, as do all employers, to act responsibly when such allegations are reported by employees. We did not take the decision to lodge a formal complaint with the FA lightly and followed the correct processes and protocols throughout," the club said.

The Clattenburg allegations have further stoked a febrile atmosphere around the game and the issue of racism, with the Society of Black Lawyers chairman, Peter Herbert, criticising Chelsea and the FA after the Metropolitan police dropped an investigation into the claims due to lack of evidence.